<!DOCTYPE html>
<html>
<head>
  <title>标题</title>
</head>
<body>
<form action="/" method="post">
    x: <input type="text" name="x" value="{{x}}" /> + y: <input type="text" name="y" value="{{y}}" /> = <input type="text" name="result" value="{{result}}" />
  <input type="submit" value="Submit" />
</form>
</body>
</html>